Sleep apnea severity is quantified by the apnea hypopnea index (AHI), which is the frequency of apnea and hypopneas per hour. In a sleep laboratory, the AHI is expressed as the frequency of apnea and hypopneas per hour of sleep. Thus, knowledge of sleep time as opposed to overall recording time is important for accurate estimation of the sleep apnea severity. Other applications to the determination of sleep time may also be relevant in conducting accurate sleep studies, as can such indication provide useful information in respect of other breathing or physiological studies that may be more or less related to sleep apnea.
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